You raise a good point.
But I don't think the reason it hasn't died out is related to whether or not it actually works.
It doesn't work.
The reason it hasn't died out is that it seems to be a kind of secular religion. Leftism argues for "fairness" and that gives its adherents a warm and fuzzy feeling (i.e., meaning to their lives). But, whenever they actually get a chance to prove their point by installing a collectivist government, they quickly learn that it won't work (Cuba, USSR, Venezuela, etc., etc., etc.).
Right now the Leftists are looking at China and saying, "See, it works in China."
What they have failed to recognize is that China has survived because it has stolen intellectual property and product designs from the U.S. On top of that, China has adopted a quasi-capitalist form of communism and that has given it a thin veneer of success.
The quasi-capitalist form of communism of which you speak is presently being destroyed by Chairman Xi and the CCP. All vestiges of that very successful but blatantly anti communist system is being systematically eliminated.
The China of which you speak, no longer is. All vestiges of free enterprise and individual entrepreneurial effort is being erased. The presence and industrial excellence of foreign companies is being or rather has been eliminated. The foreigners, their money and their brains are or very soon will be gone.
Xi is forcing a return to a purer socialist, communist, state. The new communism is based on the corporate industrial communes that provide all the citizens need for life. The corporations are all CCP controlled but offer a degree of independence from pure government control.
The transition is now, in full force tearing asunder what was. All that was isn’t and will not be. The Transition in China is a tragedy so great it is immeasurable.
We might be developing some confusion here. I don’t mean leftism works. I mean the individual strategy that liberal\weak people use works.
Specifically that weak/nonproductive people use to influence people who are productive and strong to help them, to give them a share of the kill. Today that equivalent would be to provide them with welfare benefits etc.
I imagine Stone Age people used ideas like pleasing the mountain gods while today they use ideas like equity or social justice. Both eras had different people, different strategies but the same goal. That the numbers on welfare,tax paid benefits like food stamps, free heath care etc are swelling sort of proves it works.
Interestingly Ayn Rand’s Novels get into this sort of philosophical questions and she wrote them nearly a century ago.